Development of Highly Potent and Selective Covalent FGFR4 Inhibitors Based on S <sub>N</sub> Ar Electrophiles
Moritz Schwarz, Maksym Kurkunov, Florian Wittlinger, Ramona Rudalska, Guiqun Wang, Martin P. Schwalm, Alexander Rasch, B.J. Wagner, Stefan Laufer, Stefan Knapp, Daniel Dauch, Matthias Gehringer
Abstract
Fibroblast growth factor receptor 4 (FGFR4) is thought to be a driver in several cancer types, most notably in hepatocellular carcinoma. One way to achieve high potency and isoform selectivity for FGFR4 is covalently targeting a rare cysteine (C552) in the hinge region of its kinase domain that is not present in other FGFR family members (FGFR1–3). Typically, this cysteine is addressed via classical acrylamide electrophiles. We demonstrate that noncanonical covalent “warheads” based on nucleophilic aromatic substitution (S N Ar) chemistry can be employed in a rational manner to generate highly potent and (isoform-)selective FGFR4 inhibitors with a low intrinsic reactivity. Key compounds showed low to subnanomolar potency, efficient covalent inactivation kinetics, and excellent selectivity against the other FGFRs, the kinases with an equivalent cysteine, and a representative subset of the kinome. Moreover, these compounds achieved nanomolar potencies in cellular assays and demonstrated good microsomal stability, highlighting the potential of S N Ar-based approaches in covalent inhibitor design.